Micro-electromechanical system devices

ABSTRACT

A micro-electromechanical system (MEMS) device can include a substrate and a first beam suspended relative to a substrate surface. The first beam can include a first portion and a second portion that are separated by an isolation joint made of an insulative material. The first and second portions can each include a first semiconductor and a first dielectric layer. The MEMS device can also include a second beam suspended relative to the substrate surface. The second beam can include a second semiconductor and a second dielectric layer to promote curvature of the second beam. The MEMS device can also include a third beam suspended relative to the substrate surface. The third beam consists essentially of a first material. The second beam is configured to move relative to the third beam in response to an acceleration along an axis perpendicular to the surface of the substrate.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. application Ser.No. 13/027,209, filed Feb. 14, 2011, which is incorporated by referenceherein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed generally to micro-electromechanicalsystem devices (MEMS devices), and more particularly to MEMS deviceshaving an integral electrical isolation structure.

2. Background Art

MEMS devices are electrical and mechanical devices that are fabricatedat substantially microscopic dimensions utilizing techniques well knownin the manufacture of integrated circuits. Present commercialapplications of MEMS devices are predominantly for pressure and inertialsensing, for example, accelerometers and gyroscopes used in hand-helddevices, for example, cell phones and video game controllers.

For example, a MEMS device that is an accelerometer can detect when thecell phone experiences acceleration such as when the phone is rotatedfrom a portrait orientation to a landscape orientation. Such a inertialsensing MEMS device can include a case or substrate, a mass resilientlyheld within the case, and a deflection sensor for measuring relativemotion between the case and the mass. When an acceleration isexperienced, the mass moves relative to the case, and the sensormeasures the deflection. In most cases, the acceleration is directlyproportional to the amplitude of the deflection. Processing steps havebeen developed to make a MEMS device having such a mass and deflectionsensor. When a MEMS device is constructed using processes such as theone disclosed in U.S. Pat. No. 6,239,473 to Adams et al., silicon beamscoated with silicon dioxide on three sides can be formed. These beamscan have an isolation joint that moves with the rest of the structure.These isolation joints enable multiple electrical signals to be routedto multiple places within a device and applied to multiple electricalcomponents such as sensors and actuators. However, MEMS devicesfabricated according to the process outlined in U.S. Pat. No. 6,239,473are susceptible to shock damage, interconnect damage, and frit sealfailure.

Shock Damage

One cause of shock damage in an inertial sensing MEMS device relates toa dielectric coating on the sidewalls of the beams. If subjected tolarge accelerations, for example, when a cell phone or game controllerstrikes the ground after being dropped, the sidewalls of the beams cancontact each other, causing the dielectric coating to wear by chippingor abrasion. During the wear process, chemical bonds between moleculesin the dielectric sidewall coatings are broken, creating an electricalcharge on the sidewall surface. Because these sidewall surfaces areoften silicon dioxide, an insulating material, the electrical charges donot dissipate quickly. The charges can persist for hours or even daysafter the mechanical shock occurred. At the size scale of MEMS devices,these charges can affect the operation of the MEMS device.

An electrical charge on the outer surface of the dielectric sidewallcoatings can causes a net force on the beam. This net force isindistinguishable from an acceleration that causes the beam to move.Therefore, a charged device produces a false acceleration signature.

Interconnect Damage

In addition to damage to the dielectric sidewall coatings, offset shiftscan also be created by a permanent plastic deformation or bend in themetal used to electrically interconnect various portions of the MEMSdevice from the application of large forces during operation. Plasticdeformation of the interconnect metal can causes the entire beam todeform, which can cause a perceived offset shift and a falseacceleration signature.

The interconnect metal can also be deformed by large temperatureexcursions. MEMS devices fabricated using the process discussed in U.S.Pat. No. 6,239,473 comprise multiple materials, for example, silicondioxide, silicon, and aluminum. Each of these materials has a differentcoefficient of thermal expansion, meaning that as the temperaturechanges, each material expands different amounts. Because the materialsare joined together, the materials all deform approximately the sameamount, causing a stress. If the stress levels are large enough, thematerials can permanently deform. Aluminum deforms easier than eithersilicon or silicon dioxide. Accordingly, when a MEMS device is subjectedto high temperatures excursions, for example, temperature excursionsduring the solder reflow cycles, the aluminum can plastically deform,causing a perceived offset shift and a false acceleration signature. Theactual amount that a device deforms depends on the structural design andthe quantity of metal used. For example, an accelerometer fabricatedusing the process discussed in U.S. Pat. No. 6,239,473 moves about 20 nmper g of acceleration. Due to the plastic deformation of the metalduring reflow, the rest position of the accelerometer may shift up to 2nm which is equivalent to a false reading of 100 mg's.

Minimizing the thickness of the interconnect metal can reduce thedeleterious effects. However, in U.S. Pat. No. 6,239,473, the metal bondpads and the metal seal ring surface are formed from the same layer ofmetal comprising the interconnect metal, and the metal bond pads and themetal seal ring surface have minimum thickness requirements to functionproperly. Thus, a solution for reducing interconnect damage is not assimple as merely reducing the thickness of the metal layer forming theinterconnect.

Seal Failures

MEMS devices such as those described in U.S. Pat. No. 6,239,473 use alid to form a hermetic seal around the beams of the substrate. The lidcan be coupled to the substrate using a frit seal that interfaces with ametal seal ring surface. If the interface between the frit seal and themetal seal ring surface is interrupted, for example, by a metal tracerunning directly under the metal seal ring surface to a bond pad, theinterface between the lid and the substrate is weakened. The interfacecan also be weakened when the metal traces are covered locally with apassivation oxide to prevent any electrical interactions with the lid orfit seal. Accordingly, when a MEMS device having an interruptedinterface between the lid's frit seal and the metal seal ring surface issubjected to excessive environmental stresses, the MEMS can fail causedby the weakened seal.

Accordingly, there is need for improved MEMS devices that can betterwithstand mechanical shocks, reduce the risk of metal interconnectdamage, and provide improved frit seals.

BRIEF SUMMARY OF THE INVENTION

In an embodiment, a MEMS device can include a substrate and a first beamsuspended relative to a surface of the substrate. The first beam caninclude a first portion and a second portion that are separated by anisolation joint. The isolation joint can be made of an insulativematerial. The first and second portions can each comprise a firstsemiconductor and a first dielectric layer. The MEMS device can alsoinclude a second beam suspended relative to the surface of thesubstrate. The second beam can include a second semiconductor and asecond dielectric layer to promote curvature of the second beam. TheMEMS device can further include a third beam suspended relative to thesurface of the substrate. The third beam consists essentially of a firstmaterial. The second beam can be configured to move relative to thethird beam in response to an acceleration along an axis perpendicular tothe surface of the substrate.

In an embodiment, a computer-program product can include acomputer-readable storage medium that contains instructions that, ifexecuted on a computing device, define a MEMS device. The MEMS devicecan include a substrate and a first beam suspended relative to a surfaceof the substrate. The first beam can include a first portion and asecond portion that are separated by an isolation joint. The isolationjoint can be made of an insulative material. The first and secondportions can each comprise a first semiconductor and a first dielectriclayer. The MEMS device can also include a second beam suspended relativeto the surface of the substrate. The second beam can include a secondsemiconductor and a second dielectric layer to promote curvature of thesecond beam. The MEMS device can further include a third beam suspendedrelative to the surface of the substrate. The third beam consistsessentially of a first material. The second beam can be configured tomove relative to the third beam in response to an acceleration along anaxis perpendicular to the surface of the substrate.

In an embodiment, a hand-held device can include a MEMS device. The MEMSdevice can include a substrate and a first beam suspended relative to asurface of the substrate. The first beam can include a first portion anda second portion that are separated by an isolation joint. The isolationjoint can be made of an insulative material. The first and secondportions can each comprise a first semiconductor and a first dielectriclayer. The MEMS device can also include a second beam suspended relativeto the surface of the substrate. The second beam can include a secondsemiconductor and a second dielectric layer to promote curvature of thesecond beam. The MEMS device can further include a third beam suspendedrelative to the surface of the substrate. The third beam consistsessentially of a first material. The second beam can be configured tomove relative to the third beam in response to an acceleration along anaxis perpendicular to the surface of the substrate.

Further features and advantages of the invention, as well as thestructure and operation of various embodiments of the invention, aredescribed in detail below with reference to the accompanying drawings.It is noted that the invention is not limited to the specificembodiments described herein. Such embodiments are presented herein forillustrative purposes only. Additional embodiments will be apparent topersons skilled in the relevant art(s) based on the teachings containedherein.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

The accompanying drawings, which are incorporated herein and form partof the specification, illustrate the present invention and, togetherwith the description, further serve to explain the principles of theinvention and to enable a person skilled in the relevant art(s) to makeand use the invention.

FIG. 1 is a top view of a MEMS device having an isolation joint that isfabricated according to an embodiment of the invention.

FIG. 2 is a top view of a MEMS device having an isolation joint that isfabricated according to an embodiment of the invention.

FIGS. 3-23 illustrate an exemplary method of making a MEMS deviceaccording to an embodiment of the invention.

The features and advantages of the present invention will become moreapparent from the detailed description set forth below when taken inconjunction with the drawings, in which like reference charactersidentify corresponding elements throughout. In the drawings, likereference numbers generally indicate identical, functionally similar,and/or structurally similar elements.

DETAILED DESCRIPTION OF THE INVENTION

It is noted that references in the specification to “one embodiment,”“an embodiment,” “an example embodiment,” etc., indicate that theembodiment described may include a particular feature, structure, orcharacteristic, but every embodiment may not necessarily include theparticular feature, structure, or characteristic. Moreover, such phrasesare not necessarily referring to the same embodiment. Further, when aparticular feature, structure, or characteristic is described inconnection with an embodiment, it is submitted that it is within theknowledge of one skilled in the art to effect such feature, structure,or characteristic in connection with other embodiments whether or notexplicitly described.

As mentioned above, the present invention is directed to improved MEMSdevices having isolation joints that can better withstand mechanicalshocks, that reduce the risk of interconnect damage, and that provide abetter fit seal. For example, MEMS devices according to embodiments ofthe present invention can better withstand mechanical shocks by removingdielectric material from portions of the MEMS device that contact eachother during shock. Removing dielectric material from such contactportions prevents electrical charges that can create forces fromforming. According to another embodiment, MEMS devices can reduce therisk of interconnect damage by forming a metal trace and a bond pad withdifferent layers of metal, which allows the metal trace to havedifferent properties than the bond pad. Additionally, other embodimentsprovide MEMS devices that have an improved frit seal because the metaltrace does not disrupt the seal. Accordingly, MEMS devices havingisolation joints that can better withstand mechanical shocks, reducesinterconnect damage, and provides a better frit seal and methods ofmaking such MEMS devices will be described.

FIG. 1 is a top view CAD drawing used to create of MEMS device 100according to an embodiment. MEMS device 100 can include a metal bond pad101 and a metal trace 104. The metal bond pad 101 can be connected tothe metal trace at connection 102. MEMS device 100 can also include ametal seal ring surface 103 for coupling with a lid (not shown). Metaltrace 104 can run underneath the metal seal ring surface 103. MEMSdevice 100 can have one or more beams, for example, beams 106, 107, and108. Beams 106, 107, and 108 can be used in inertial sensing MEMSdevices such as those described in U.S. Pat. No. 7,430,909 to Adams etal., the entirety of which is hereby incorporated by reference herein.

FIG. 2 is a top view of a MEMS device according to another embodiment.In this embodiment, metal seal ring surface 103 is continuous—metal sealring surface 103 completely surrounds the entire beam structure 110,which can include one or more beams. Accordingly, a continuous,uninterrupted seal can be formed about beam structure 110.

The MEMS devices 100 illustrated in FIGS. 1-2 are embodiments presentedherein for illustrative purposes only. The invention is not limited tothe specific embodiments illustrated in FIGS. 1-2. For example, a MEMsdevice can have a beam structure comprising any number of beams and beamconfigurations, and multiple beams can have isolation joints.

FIGS. 3-23, which illustrate a cross section of MEMS device 100 alongline 3-3, disclose embodiments of making MEMS device 100. In FIG. 3, anisolation trench 121 can be formed in a substrate 120. The substrate canbe, for example, a silicon wafer that is boron doped to 5 mOhm-cm with a<100> stallographic orientation. Doping levels, resistivity, andcrystallographic orientation, however, can vary. The substrate 120 canalso have a dielectric layer, for example, silicon dioxide (not shown).For example, substrate 120 can be thermally oxidized to form a 500 nmoxide mask layer; however, any other suitable method can be used such aschemical vapor deposition (CVD).

In an embodiment, isolation trench 121 can be formed using any suitablelithographic technique, for example, photolithography, electron-beamlithography, imprint lithography, and any other suitable form oflithography. A resist (not shown) can be spun onto substrate 120, and anisolation trench pattern can be defined in the resist and the oxide masklayer (if present) using, for example, a plasma dry etch in CHF₃ and O₂.The isolation trench pattern can be transferred to substrate 120 to formisolation trench 121 where isolation joint 105 will be formed. In oneembodiment, a silicon etch chamber running the Bosch process thatalternates between etching (for example, SF₆ etching) and passivation(for example, using C₄F₈) can be used to form the isolation trench 121.After the substrate 120 is etched, the resist and oxide mask layer canbe removed using any suitable technique. Isolation trench pattern 121can have any suitable profile, for example, a reentrant profile in whichthe top is narrower than the bottom as illustrated in FIG. 3. Anembodiment includes a profile that monotonically increases in width.

As illustrated in FIG. 4, isolation trench 121 can be filled with adielectric material 123, for example, silicon dioxide or any othersuitable dielectric material. In an embodiment, a silicon wafer can bethermally oxidized to form a layer of silicon dioxide. The silicon wafercan be oxidize at approximately 1100 C to 1200 C with wet oxidation toform silicon dioxide having a thickness of about 1.5 to 2.5 μm. Anopening 124 of isolation trench 121 can be sealed, and a void 125 mayremain after the oxidization process.

Optionally, any divots in the dielectric layer 123 at opening 124 can beplanarized. For example, a resist-based planarization can be used toreduce or eliminate a divot at opening 124. During such a planarizationstep, dielectric layer 123 on top of the substrate 120 can be reduced toa thickness of about 0.5 μm to 1.5 μm. However, this thickness can varybased on the particular MEMS device being fabricated. Although a resistplanarization is described, other suitable planarization techniques canbe used, for example, chemical mechanical polishing.

As illustrated in FIG. 5, an opening or via 130 can be formed indielectric layer 123. Any suitable lithographic technique, for example,photolithography, and dry etching can be used to define via 130 indielectric layer 123. Via 130 can be used to electrically couple thesubstrate 120 to a subsequent metal layer. Optionally, the surface ofsubstrate 120 exposed at via 130 can by prepared for such an electricalcoupling by forming a layer of oxide on the exposed surface, forexample, by thermally and dry oxidizing substrate 120 at about 850 C to950 C to form about 100 A of oxide. This oxide layer can then be dippedoff in liquid HF prior to forming a metal layer over the top of theexposed surface of substrate 120.

Subsequently, as illustrated in FIG. 6, a metal layer 140 can be formed.In an embodiment, metal layer 140 can have a thickness of about 2500 Ato 3500 A. In other embodiments, the thickness of metal layer 140 can beformed as thin as possible without compromising the structuralintegrity. Metal layer 140 can be aluminum, titanium nitride,aluminum-silicon, aluminum-silicon-copper, or any other suitable metalor alloy.

In an embodiment, metal layer 140 can be patterned to define the metaltrace 104 that serves as an interconnect layer on the MEMS device thatruns along beam 106 as illustrated in FIG. 7. Metal trace 104 caninclude a proximal end portion 142 and a distal end portion 144.Proximal end portion 142 can form connection 102 with the metal bond pad101 as illustrated in FIG. 14 and described below. Distal end portion144 can be electrically coupled to a distal portion of substrate 120through via 130. Metal trace 104 can be formed using any suitablelithographic technique, for example, photolithography, and metaletching.

As shown in FIG. 8, a dielectric passivation layer 160 can be formed,covering metal trace 104 and dielectric layer 123 on substrate 120.Dielectric passivation layer 160 can protect metal trace 104 duringsubsequent etching steps. In an embodiment, passivation layer 160 can bea TEOS oxide that is deposited at a high power to promote a higherdensity film, which better resists etching. In one example, a TEOS oxidecan be deposited using an AMAT P5000 deposition tool running at about400 C with approximately 1100 W of RF power, at approximately 8.2 mTorrpressure, with flow rates of approximately 1000 mg/min of TEOS,approximately 1000 sccm of O₂, and approximately 1000 sccm of He.Passivation layer 160, however, can be any suitable dielectric material.

As shown in FIG. 9, portions of dielectric passivation layer 160 can beremoved. For example, if passivation layer 160 is an oxide, passivationlayer 160 can be patterned using any suitable lithographic technique,for example, photolithography, and etched with dry oxide etching. In anembodiment, patterned dielectric passivation layer 160 can include abase 170 for the metal seal ring surface 103 (see FIG. 14) and remnants172 that persist adjacent to topography changes created by metal trace104. In one example, dielectric passivation layer 160 is patterned andetched to expose distal end portion 142 of metal trace 104 fromunderneath dielectric passivation layer 160.

In an embodiment, any residue formed on substrate 120 from etchingdielectric passivation layer 160 can be removed. For example, during adry etch, residual polymers can form on vertical surfaces, and standardtechniques for removing the resist used during the dry etch do notremove all of the residual polymers. Such polymers can produce unwantedfeatures such as inhibition of subsequent etching, variability in etchrates, and irregular sheets of residual material that can peel off andobstruct beam movement. In one example, the residual polymers can beremoved using REZI-78 residue removers. In one embodiment, the removalstep can be followed with a spin-rinse-dry cycle.

Next, as shown in FIG. 10, an opening 180 can be formed in dielectriclayer 123 on the distal side of substrate 120. Opening 180 can be formedusing any suitable lithographic technique, for example,photolithography, and dry oxide etching. In one embodiment, opening 180corresponds to the top of a beam, for example, beam 108 (see FIG. 16).In an embodiment, any residue formed on the substrate 120 while etchingdielectric material layer 123 can removed.

A second dielectric passivation layer 190 can be formed as shown in FIG.11. For example, second dielectric passivation layer 190 can be a TEOSoxide having a thickness of about 4500 A to 5500 A. The TEOS oxide canbe deposited at a lower power than at which passivation layer 160 wasdeposited, for example, 900W of RF power, so that passivation layer 190is more susceptible to subsequent etching steps than passivation layer160. Although second dielectric passivation layer 190 is described aboveas a TEOS oxide, passivation layer 190 can be other suitable dielectricmaterials. Passivation layer 190 can be an inter-metal dielectric layerthat insulates metal trace 104 from subsequent layers of metal to beformed. Passivation layer 190 can also be used as a mask to pattern abeam such as beam 108 (see FIG. 16).

As shown in FIG. 12, passivation layer 190 can be patterned and etched.In an example, an opening or via 200 can be formed in the dielectricpassivation layer 190, exposing a surface of dielectric layer 123 andproximal end portion 142 of metal trace 104. Any suitable lithographictechnique, for example, photolithography, and etching can be used toform via 200. In one embodiment, any residue remaining from etchingpassivation layer 190 can be removed.

Next, a second metal layer 210 can be formed on the substrate 120 asshown in FIG. 13. Dielectric passivation layer 190 can be between secondmetal layer 210 and metal trace 104 except at exposed portion 142 of themetal trace 104. Second metal layer 210 can be aluminum, titaniumnitride, aluminum-silicon, aluminum-silicon-copper, or any othersuitable metal or alloy. For example, second metal layer 210 can be purealuminum having a thickness of about 6500 A to 7500 A or any othersuitable thickness to form metal bond pad and to form an interface forsealing with a glass fit.

As shown in FIGS. 12 and 13, second metal layer 210 can be patterned andetched. In one embodiment, a metal bond pad 101 and a metal seal ringsurface 103 can be formed. In an embodiment, second metal layer 210 canbe patterned such that the metal seal ring surface 103 surrounds thebeam structure of MEMS device 100, creating a continuous seal whencoupled to a lid (see FIGS. 22-23). In an example, second metal layer210 can be patterned using any suitable lithographic technique and metaletching, for example, a wet or dry aluminum etching. In an embodiment,an opening or gap 212 can be formed. Gap 212 is between the metal sealring surface 103 and connection 102 of metal trace 104 and bond pad 101.Gap 212 can allow a lid to be coupled to the metal seal ring surface 103without metal trace 104 or metal bond pad 101 running immediately belowthe lid, which would disrupt the seal between the lid and the metal sealring surface 103. This configuration can improve the seal strength.

In an embodiment, first metal layer 140 can form metal trace 104, andsecond material layer 210 can form metal bond pad 101 and metal sealring surface 103. Using two layers of metal, allows metal trace 104 tohave a different thickness than the bond pad 101 and metal seal ringsurface 103. For example, in an embodiment, the thickness of first metallayer 140 is smaller than the thickness of the second metal layer 210.Accordingly, metal trace 104 that runs along a beam can be thin, whichminimizes the influence of metal trace 104 on a beam despite the amountof plastic deformation that occurs from bending caused by an appliedforce or the fabrication process. Meanwhile, metal bond pad 101 andmetal seal ring surface 103 can be thick, which promotes a durable fritseal with a lid at metal seal ring surface 103 and electricalconnections at bond pad 101.

To protect metal bond pad 101 and metal seal ring surface 103 fromsubsequent etching, a dielectric passivation layer 230 can be formed onthe substrate 120, covering at least metal bond pad 101 and metal sealring surface 103 as shown in FIG. 14. In an embodiment, dielectricpassivation layer 230 can be a TEOS oxide deposited to a thickness ofapproximately 1,500 A to 2,500 A. In one embodiment, the TEOS oxide canbe deposited at low power, for example, approximately 900 W of RF power,to promote a later etching step.

As shown in FIG. 16, substrate 120 can be patterned and etched to createat least one trench that can define a profile of a beam. For example,trenches 242, 244, and 246 can be formed in substrate 120 to define theprofiles of beams 106, 107, and 108. In one embodiment, trenches 242,244, and 246 can be formed by using any suitable lithographic technique,for example, photolithography, and a series of dry etching steps thatetch dielectric passivation layer 230, dielectric passivation layer 190,dielectric layer 123, and substrate 120. In one example, a standardplasma dry etch using CHF₃ and O₂ can be used to etch dielectricpassivation layer 230, dielectric passivation layer 190, and dielectriclayer 123. In an embodiment, substrate 120 can be etched using a siliconetch chamber running the Bosch process. In another embodiment, metaltrace 104 can be etched if it is within the masking stack. In yetanother embodiment, any residue remaining from etching passivation layer230, passivation layer 190, dielectric layer 123, and substrate 120 canbe removed.

FIG. 17 shows an embodiment in which a fourth dielectric layer 250 canbe formed on the substrate 120, covering at least the sidewalls 251 andfloors 252 of the trenches 242, 244, and 246 formed in substrate 120.The fourth dielectric layer 250 can be an oxide. In one embodiment, theoxide is a TEOS oxide deposited at a low power, for example,approximately 1000 W of RF power.

As shown in FIG. 18, portions of dielectric layer 250 that are formed ontrench floors 252 can be removed. For example, an oxide layer 250 ontrench floors 252 can be removed with an anisotropic dry oxide etch,exposing surfaces of substrate 120. In an embodiment, any residue formedon sidewalls 251 by the dry etch can be removed. By removing the residueon sidewalls 251, portions of dielectric layer 250 remaining onsidewalls 251 can be more easily removed in a subsequent etching stepbecause such residues would inhibit a subsequent etch.

Next, as shown in FIG. 19, the depth of trenches 242, 244, and 246 canbe extended by further etching substrate 120. In an example, a siliconsubstrate 120 can be etched using an anisotropic silicon extension etch.The resulting regions 270 of trenches 242, 244, and 246 can havesidewalls without dielectric layer 250. In one example, the depth ofexposed regions 270 can be about 2 μm to 15 μm. The depth, however, canvary depending on the desired width of the beams 106, 107, and 108. Thedepth of exposed portions 270 can help define the distance between theresulting silicon beams 106, 107, and 108 and the floor of the substrate120. In one embodiment, the residue formed from the silicon extensionetch is not removed so that the wafer can be directly transitioned to arelease etch, as described below, without venting the etch chamber,which can reduce the amount of native oxides that form on the substratesurface and can reduce any disruption to the initiation andreproducibility of the release etch. Alternatively, the residue can beremoved.

Next, at least one beam can be formed. For example, beams 106, 108, and109 can be formed by a release etch. FIG. 20 shows an exemplary MEMSdevice after a release etch, for example, a dry isotropic siliconrelease etch such as a plasma etcher using SF₆. The release etch cancreate a cavity 280 that separates beams 106, 107, and 108 from a floor282 of the substrate 120, thereby allowing beams 106, 107, and 108 toflex or move during operation of MEMS device 100. In an embodiment,after the release etch, beams 106 and 107 can have dielectric layer 123and passivation layer 190 on top, while beam 108 can have onlydielectric passivation layer 190 on top due to the opening 180 formed inoxide layer 123 during a prior processing step.

In one embodiment, portions of dielectric layer 250 that are formed onthe sidewalls of beams 106, 107, and 108 can be removed as shown in FIG.21. For example, these portions of dielectric layer 250 can be removedusing a hydrogen fluoride (HF) vapor etching system such as a PRIMAXXsystem for approximately 4 minutes. Removing these portions ofdielectric layer 250 on sidewalls 251 of beams 106, 107, and 108 can beadvantageous. As discussed above, if there is a dielectric layer onsidewalls 251, electrical charges can develop in the sidewall coatingswhen the beams contact each other during operation of the MEMS device.By removing dielectric layer 250, the outer surface of sidewalls 251comprises silicon, a semiconductor, and not a dielectric material.Accordingly, any electrical charges created from beam contact candissipate quickly, which helps prevent a force from being applied to thebeams. In an embodiment, the HF vapor etch is controlled so that etchingof isolation joint 105 is reduced. If the HF vapor etch is uncontrolled,isolation joint 105 can be weakened since it can comprise silicondioxide like dielectric layer 250. However, when isolation joint 105 ismade from thermal oxide, isolation joint 105 etches at a slower ratethan dielectric layer 250.

In another embodiment, dielectric layer 250 and passivation layer 190can be removed from the top of the substrate during the HF vapor etch,exposing bond pad 101 and gap 212 around metal seal ring surface 103.This removal allows for wire bonding with the bond pad 101 and a lid toseal with the metal seal ring surface 230. In another embodiment,passivation layer 190 on top of beams 107 and 108 is removed during theHF vapor etch.

In one embodiment, the thickness of dielectric layer 250 and passivationlayer 190 can be minimized to reduce the etching of the isolation joint105 during the HF vapor etch. For example, the thickness of dielectriclayer 250 and passivation layer 190 can be less than about 450 nm, andpreferably less than about 400 nm. Any thickness below about 450 nm canminimize the etching effect on isolation joint 105. In anotherembodiment, an antistiction coating can be applied to help prevent beams106, 107, and 108 from sticking during operation of the MEMS device.

As shown in FIG. 22, a lid 300 can be coupled to the device at metalseal ring surface 103. Lid 300 can form a hermetic seal with thesubstrate 120. Lid 300 can include a metal seal region 305. In anembodiment, metal, seal region 305 can be, for example, aluminumdeposited at 7,000 A. The metal seal region 305 can be patterned andetched using any suitable lithographic technique, for example,photolithography, and metal etching. Lid 300 can also have a bump stop304 that prevents over flexing of one or more beams, for example, beam108. Bump stop 304 can be formed by using any suitable lithographictechnique, for example, photolithography, and silicon etching, forexample, an anisotropic dry silicon etching, to define a recess 302. Lid300 can also have a recess 303 along an outer edge defining a channel306. Recess 303 can be formed using a wafer dicing saw to facilitate theremoval of the channel silicon. A glass frit 310 can be formed on lid300 by, for example, using a screen printer and a furnace heated up toabout 420 C.

Lid 300 can be bonded with the substrate 120 by, for example, using astandard wafer bonder such as an EVG 501 bonder. After bonding, channel306 can be removed to expose bond pad 101. Channel 306 can be removed byany suitable means, for example, a wafer dicing saw. The wafer dicingsaw can be aligned using a preexisting pattern on the top of lid 300, orusing an IR dicing saw that can see alignment marks through the lid onthe lower side of the wafer. FIG. 23 shows lid 300 with channel 306removed.

In another embodiment, a MEMS device can have a beam with an integratedisolation joint and a metal trace, for example, beam 106; a beam havingan dielectric coating on top, for example, beam 107; a beam comprisingonly silicon, for example, beam 108; or any combination thereof. Beamshaving an isolation joint and a metal trace are useful in complex MEMSdevices requiring multiple electrical potentials such as gyroscopes asin U.S. Pat. No. 6,626,039. Beams having a dielectric coating on top areuseful for devices needing bowed beams, such as those described in U.S.Pat. No. 7,430,909, for enabling out-of-plane capacitive sensors. Beamscomprising only silicon are useful for inertial sensors having surfacesthat will impact and potentially charge if made or coated with adielectric material.

EXAMPLES SOFTWARE IMPLEMENTATIONS

In addition to hardware implementations of MEMS devices described above,such MEMS devices may also be embodied in software disposed, forexample, in a computer usable (e.g., readable) medium configured tostore the software (e.g., a computer readable program code). The programcode causes the enablement of embodiments of the present invention,including the fabrication of MEMS devices disclosed herein.

For example, this can be accomplished through the use of generalprogramming languages (such as C or C++), hardware description languages(HDL) including Verilog HDL, VHDL, Altera HDL (AHDL) and so on, or otheravailable programming and/or schematic capture tools (such as circuitcapture tools). The program code can be disposed in any known computerusable medium including semiconductor, magnetic disk, optical disk (suchas CD-ROM, DVD-ROM) and as a computer data signal embodied in a computerusable (e.g., readable) transmission medium (such as a carrier wave orany other medium including digital, optical, or analog-based medium). Assuch, the code can be transmitted over communication networks includingthe Internet and intranets. It is understood that the functionsaccomplished and/or structure provided by the systems and techniquesdescribed above can be embodied in program code and may be transformedto hardware as part of the production of MEMS devices.

What is claimed:
 1. A micro-electromechanical system (MEMS) device,comprising: a substrate; a first beam suspended relative to a surface ofthe substrate, the first beam comprising a first portion and a secondportion that are separated by an isolation joint, the isolation jointcomprising an insulative material, wherein the first and second portionseach comprise a first semiconductor and a first dielectric layer; asecond beam suspended relative to the surface of the substrate, thesecond beam comprising a second semiconductor and a second dielectriclayer to promote curvature of the second beam; and a third beamsuspended relative to the surface of the substrate, the third beamconsisting essentially of a first material; wherein the second beam isconfigured to move relative to the third beam in response to anacceleration along an axis perpendicular to the surface of thesubstrate.
 2. The MEMS device of claim 1, wherein the first materialcomprises a third semiconductor.
 3. The MEMS device of claim 2, whereinthe first, second, and third semiconductors are silicon.
 4. The MEMSdevice of claim 1, wherein each of the first, second, and third beamshas a profile defining a side wall, and wherein the side wall of each ofthe first, second, and third beams has substantially no dielectric layerdisposed thereon.
 5. The MEMS device of claim 1, further comprising anelectrically conductive trace that is mechanically coupled to the firstbeam and electrically coupled to the first semiconductor of the secondportion but not the first semiconductor of the first portion.
 6. TheMEMS device of claim 5, wherein the electrically conductive tracecomprises a metal.
 7. The MEMS device of claim 1, wherein the movementof the second beam relative to the third beam is used in acapacitance-based displacement transducer.
 8. A computer-program productcomprising a computer-readable storage medium containing instructionsthat, if executed on a computing device, define amicro-electromechanical device comprising: a substrate; a first beamsuspended relative to a surface of the substrate, the first beamcomprising a first portion and a second portion that are separated by anisolation joint, the isolation joint comprising an insulative material,wherein the first and second portions each comprise a firstsemiconductor and a first dielectric layer; a second beam suspendedrelative to the surface of the substrate, the second beam comprising asecond semiconductor and a second dielectric layer to promote curvatureof the second beam; and a third beam suspended relative to the surfaceof the substrate, the third beam consisting essentially of a firstmaterial; wherein the second beam is configured to move relative to thethird beam in response to an acceleration along an axis perpendicular tothe surface of the substrate.
 9. The computer-program product of claim8, wherein the first material comprises a third semiconductor.
 10. Thecomputer-program product of claim 9, wherein the first, second, andthird semiconductors are silicon.
 11. The computer-program product ofclaim 8, wherein each of the first, second, and third beams has aprofile defining a side wall, and wherein the side wall of each of thefirst, second, and third beams has substantially no dielectric layerdisposed thereon.
 12. The computer-program product of claim 8, whereinthe micro-electromechanical device further comprises an electricallyconductive trace that is mechanically coupled to the first beam andelectrically coupled to the first semiconductor of the second portionbut not the first semiconductor of the first portion.
 13. Thecomputer-program product of claim 12, wherein the electricallyconductive trace comprises a metal.
 14. The computer-program product ofclaim 8, wherein the movement of the second beam relative to the thirdbeam is used in a capacitance-based displacement transducer.
 15. Ahand-held device comprising: a micro-electromechanical system (MEMS)device comprising: a substrate; a first beam suspended relative to asurface of the substrate, the first beam comprising a first portion anda second portion that are separated by an isolation joint, the isolationjoint comprising an insulative material, wherein the first and secondportions each comprise a first semiconductor and a first dielectriclayer; a second beam suspended relative to the surface of the substrate,the second beam comprising a second semiconductor and a seconddielectric layer to promote curvature of the second beam; and a thirdbeam suspended relative to the surface of the substrate, the third beamconsisting essentially of a first material; wherein the second beam isconfigured to move relative to the third beam in response to anacceleration along an axis perpendicular to the surface of thesubstrate.
 16. The hand-held device of claim 15, wherein the firstmaterial comprises a third semiconductor.
 17. The hand-held device ofclaim 16, wherein the first, second, and third semiconductors aresilicon.
 18. The hand-held device of claim 15, wherein the movement ofthe second beam relative to the third beam is used in acapacitance-based displacement transducer.